The influence of the hypothalamic releasing factors CRF and GRF on the hormonal secretion of pituitary adenomas has been determined in vitro and correlated with the patients' response in vivo. These studies indicate that the pituitary tumors causing Cushing's disease, Nelson's Syndrome and acromegaly are responsive to their appropriate releasing factor. We are also investigating the influence of the releasing factors on the rate of growth of pituitary tumors in vitro. By understanding the mechanism of the secretary responses of these tumors to the releasing factors, new therapeutic methods may evolve.